Piezoelectric body manufacturing method, piezoelectric body, ultrasonic probe, ultrasonic diagnosing device, and nondestructive inspection device

ABSTRACT

Herein disclosed are a piezoelectric device, an ultrasonic probe, an ultrasonic diagnostic apparatus, a nondestructive testing device, and a method of producing one or more piezoelectric devices respectively having predetermined thickness distributions equal in shape to one another with high precision to realize an ultrasound diagnosis with high reliability. The method of producing one or more piezoelectric devices comprises a molding process of: molding a mixture of raw materials including piezoelectric ceramic powders and a binding agent immersed in a solvent to form a plurality of sheet-like raw material elements  6  each having a thickness in a range of a few ten microns to a few hundred microns by way of, for example, a Doctor Blade technique, a laminating process of laminating a plurality of sheet-like raw material elements  6  to obtain a piezoelectric element  7 , a pressing process of imparting pressing forces to the piezoelectric element  7  to obtain a piezoelectric element  7   a  having a predetermined shape, and a burning process of burning the piezoelectric element  7   a.

TECHNICAL FIELD

The present invention relates to a method of producing a piezoelectricdevice available for diagnosis, treatment, nondestructive testing, orthe like, and more particularly to a piezoelectric device, an ultrasonicprobe, an ultrasonic diagnostic apparatus, and a nondestructive testingdevice.

BACKGROUND ART

The conventional ultrasonic probe of this type is shown in FIG. 24 ascomprising a piezoelectric device 1 having a thickness concavely curvedin a manner that the thickness of the piezoelectric device 1 graduallyincreases from a center portion toward end portions along the minoraxis, an acoustic matching layer 2 having a thickness concavely curvedin accordance with that of the piezoelectric device 1 with a result thatthe thickness of the acoustic matching layer 2 gradually increases froma center portion toward end portions along the minor axis to ensure thatan ultrasonic wave is efficiently transmitted and received, an acousticlens 3 for converging the ultrasonic wave on one fixed focal point withrespect to the minor direction, and a rearward load 4, placed rearwardof the piezoelectric device 1, for carrying out an acoustic dampingoperation. The ultrasonic wave emitted from the piezoelectric device 1varies in frequency spectrum in accordance with the thickness of thepiezoelectric device 1 resulting in the fact that the frequency spectrumof the ultrasonic wave tends to shift to a higher frequency range as thethickness of the piezoelectric device 1 decreases (as disclosed inJapanese Patent Laid-Open Publication No. 58-29455).

The above-mentioned piezoelectric device 1 having a thickness graduallyvaried along the minor axis is operative to vibrate at a frequencygradually varied in accordance with the thickness of the piezoelectricdevice 1 in a manner that the frequency of the vibration of thepiezoelectric device 1 gradually decreases from the center portiontoward the end portions along the minor axis. Furthermore, the effectiveaperture of the piezoelectric device 1 is gradually varied in accordancewith the thickness of the piezoelectric device 1 in a manner that theeffective aperture of the piezoelectric device 1 gradually increasesfrom the center portion where the piezoelectric device 1 vibrates at ahigh frequency toward the end portions where the piezoelectric device 1vibrates at a frequency lower than that of the center portion.Accordingly, an ultrasonic diagnostic apparatus such as for example anondestructive testing device equipped with the piezoelectric device asshown in FIG. 24 can generate a thin ultrasound beam at a short focaldistance in the case that high frequency components of the ultrasonicwave are extracted, and generate a thin ultrasound beam at a long focaldistance in the case that low frequency components of the ultrasonicwave are extracted. This leads to the fact that the ultrasonicdiagnostic apparatus equipped with the piezoelectric device as shown inFIG. 24 can generate thin ultrasound beams from a short distance to along distance by stepwise changing the frequency components of theultrasonic wave to be extracted, thereby improving its azimuthresolution.

One method of producing a piezoelectric device of this type comprisesthe step of carrying out a grinding processing on materials of thepiezoelectric device with a disc-shaped grinding wheel 5 as shown inFIG. 25 (as disclosed in Japanese Patent Laid-Open Publication No.07-107595). The grinding wheel 5 has a width equal to that of thepiezoelectric device 1 and has such a shape that the piezoelectricdevice 1 with a desired thickness distribution can be ground as a resultof the grinding processing. The grinding wheel 5 is designed to movealong a Y-axis direction to grind the materials while rotating around arotation axis parallel to an X-axis parallel to a plane bottom surfaceof the piezoelectric device 1.

Another method of producing a piezoelectric device of this typecomprises the steps of rotating the grinding wheel 5 around a rotationaxis inclined to the X-axis in a manner that an edge of the grindingwheel 5 is held in contact with the surface of the piezoelectric device1 as shown in FIG. 26, and repeatedly grinding the material with theedge of the grinding wheel 5 while the grinding wheel 5 is movingbetween two end portions of the piezoelectric device 1 along the X-axis.The position of the grinding wheel 5 is controlled with respect to aZ-axis direction so that the piezoelectric device 1 having a desiredthickness distribution can be ground as a result of the grindingprocessing (as disclosed in Japanese Patent Laid-Open Publication No.07-107595). The grinding wheel 5 is designed to repeatedly move alongthe Y-axis direction while caring out the above-mentioned grindingprocessing on the materials with a result that the piezoelectric device1 is thus ground along the Y-axis.

The conventional ultrasonic probe as previously mentioned, however,encounters a drawback that the piezoelectric device is quite easy to becracked by the reason that the thickness of the piezoelectric device isrequired to be several hundred μm in the case that the conventionalultrasonic probe is for use in, for example, an ultrasonic diagnosticapparatus, and the piezoelectric device is designed to emit anultrasonic wave of several MHz, and made of a ground piezoelectricceramic such as for example PZT (lead zirconate titanate).

The conventional ultrasonic probe encounters another drawback that adistance between electrodes respectively placed on a first surface ofthe piezoelectric device and a second surface of the piezoelectricdevice opposite to the first surface of the piezoelectric device acrossthe thickness of the piezoelectric device tends to be uneven by thereason that the thickness of the piezoelectric device constituting theconventional ultrasonic probe is uneven. The unevenness of the distancebetween the electrodes causes electric field strength and thuspolarization state to be uneven in the event that a power voltage isapplied to the piezoelectric device to polarize the piezoelectricdevice. The fact that an electric field applied to the thin centerportion is greater than an electric field applied to the end portionwhile the piezoelectric device is polarized leads to the fact that thepiezoelectric device is caused to be distorted, thereby making it easierfor the piezoelectric device to be cracked while the piezoelectricdevice is polarized. Furthermore, the fact that the electric fieldapplied to the thin center portion is greater than the electric fieldapplied to the end portion while the piezoelectric device is drivenleads to the fact that the piezoelectric device is caused to bedistorted, thereby making it easier for the piezoelectric device to becracked while the conventional ultrasonic probe is driven.

The conventional method of producing a piezoelectric device encounters adrawback that a thin portion of the piezoelectric device is difficult tobe ground by the reason that the conventional method comprises the stepof carrying out a grinding processing on materials of the piezoelectricdevice. As the ultrasonic diagnostic apparatus is required to emit anultrasonic wave of a higher frequency such as, for example, severaldozen MHz, it becomes more difficult to grind the thin portion of thepiezoelectric device. Furthermore, in the case that the width of thepiezoelectric device is required to be uneven in addition to thethickness of the piezoelectric device, the end portions of thepiezoelectric device are required to be ground accordingly. Assumingthat the thickness of the piezoelectric device is several hundred μm atthe end portion, a grinding tool such as, for example, a grinding wheel5 is required to be minute in size equal to or less than several hundredμm, and it is extremely difficult to carry out a grinding processing onmaterials of the piezoelectric device. It is also extremely difficult toconstantly produce a plurality of piezoelectric devices equal in shapeto one another with high precision.

The present invention is made for the purpose of overcoming theabove-mentioned conventional drawbacks and is directed to a method ofproducing a plurality of piezoelectric devices having a thicknessdistribution equal in shape to one another with high precision, and moreparticularly to an ultrasonic probe, an ultrasonic diagnostic apparatus,and a nondestructive testing device.

DISCLOSURE OF INVENTION

In accordance with the present invention, there is provided a method ofproducing a piezoelectric device, comprising the steps of: (a) moldingone or more raw material elements including at least one piezoelectricmaterial to form a predetermined piezoelectric element; and (b)imparting pressing forces to the piezoelectric element to have thepiezoelectric element molded into a predetermined shape. The methodmakes it possible for a manufacturer to produce a piezoelectric devicehaving a predetermined uneven thickness distribution with ease, whileeliminating the need of carrying out any technically-difficult minutemachining processing such as for example a grinding processing.Furthermore, a plurality of piezoelectric devices equal in shape to oneanother can be constantly produced with high precision resulting fromthe fact that the shape of a die is simply transferred to them.

In the aforementioned method of producing a piezoelectric device, thestep (a) may have a step of laminating a plurality of sheet-like rawmaterial elements respectively having thicknesses collectively inaccordance with a thickness distribution of the piezoelectric device.The method makes it possible for a manufacturer to produce apiezoelectric device having a desired thickness distribution withincreased flexibility.

In the aforementioned method of producing a piezoelectric device, thestep (a) may have a step of laminating the number and shapes ofsheet-like raw material elements in accordance with a thicknessdistribution of the piezoelectric device. The method makes it possiblefor a manufacturer to produce a piezoelectric device having desiredshape and thickness distribution with increased flexibility.

In the aforementioned method of producing a piezoelectric device, thestep (a) may have a step of laminating one or more sheet-like rawmaterial elements respectively having widths collectively in accordancewith a thickness distribution of the piezoelectric device. The methodmakes it possible for a manufacturer to produce a piezoelectric devicehaving desired shape and width distribution with increased flexibility.Preferably, one or more sheet-like raw material elements respectivelyformed with through bores should be laminated. More preferably, one ormore sheet-like raw material elements should be laminated in a mannerthat the through bores of the one or more sheet-like raw materialelements in size collectively corresponds to a thickness distribution ofthe piezoelectric device.

In accordance with the present invention, there is provided a method ofproducing a piezoelectric device, comprising the steps of: (c) producinga first piezoelectric body having a non-plane first surface and a planesecond surface opposite to the first surface, and a second piezoelectricbody having a plane first surface and a plane second surface opposite tothe first surface, the second piezoelectric body having electrodesrespectively on the first and second surfaces; and (d) fixedlyconnecting the first piezoelectric body to the second piezoelectric bodywith the second surface of the first piezoelectric body held in contactwith the first surface of the second piezoelectric body. The methodmakes it possible for a manufacturer to produce a piezoelectric device,in which an electric field strength applied to the piezoelectric devicemaintains constant. This leads to the fact that the polarization stateof the piezoelectric device maintains constant as well as thepiezoelectric device is kept from being excessively distorted so thatthe piezoelectric device is not cracked.

In accordance with the present invention, there is provided apiezoelectric device comprising a piezoelectric element having one ormore raw material elements including a piezoelectric material, in whichpressing forces have been imparted to the piezoelectric element to havethe piezoelectric element molded. The present invention makes itpossible for a manufacturer to produce a piezoelectric device having apredetermined uneven thickness distribution with ease, while eliminatingthe need of carrying out any technically-difficult minute machiningprocessing such as for example a grinding processing. Furthermore, aplurality of piezoelectric devices equal in shape to one another can beconstantly produced with high precision because of the fact that theshape of the die is simply transferred to them.

In the aforementioned piezoelectric device, the piezoelectric elementmay have a plurality of sheet-like raw material elements respectivelyhaving thicknesses and laminated in accordance with a thicknessdistribution of the piezoelectric device. The present invention makes itpossible for a manufacturer to produce a piezoelectric device having adesired thickness distribution with increased flexibility by adaptivelylaminating a plurality of sheet-like raw material elements respectivelyhaving thicknesses collectively in accordance with the thicknessdistribution of the piezoelectric device.

In the aforementioned piezoelectric device, the piezoelectric elementmay have a plurality of sheet-like raw material elements respectivelyhaving thicknesses and formed with through bores, and laminated inaccordance with a thickness distribution of the piezoelectric device.The present invention makes it possible for a manufacturer to produce apiezoelectric device having shape and desired thickness distributionswith increased flexibility.

In the aforementioned piezoelectric device, the piezoelectric elementmay have a sheet-like raw material element formed with a through bore insize in accordance with a thickness distribution of the piezoelectricdevice. The present invention makes it possible for a manufacturer toproduce a piezoelectric device having desired shape and widthdistribution with increased flexibility. Preferably, one or moresheet-like raw material elements should be laminated in a manner thatthe through bores of the one or more sheet-like raw material elements insize collectively corresponds to a thickness distribution of thepiezoelectric device.

In the aforementioned piezoelectric device, the piezoelectric elementmay have a plurality of laminated sheet-like raw material elements and aplurality of electrodes spaced apart from each other at a predetermineddistance. The present invention makes it possible for an electric fieldstrength applied to the piezoelectric device to maintain constant,thereby resulting in the fact that the polarization state of thepiezoelectric device maintains constant as well as the piezoelectricdevice is kept from being excessively distorted so that thepiezoelectric device is not cracked. Furthermore, the piezoelectricdevice according to the present invention, which has a constructionproduced through the steps of laminating a plurality of sheet-like rawmaterial elements respectively having thicknesses collectively inaccordance with a thickness distribution of the piezoelectric device toproduce a piezoelectric element, and imparting pressing forces to thepiezoelectric element to have the piezoelectric element molded into apredetermined shape, makes it possible for a manufacturer to produce apiezoelectric device having a predetermined uneven thicknessdistribution with ease, while eliminating the need of carrying out anytechnically-difficult minute machining processing such as for example agrinding processing. Furthermore, a plurality of piezoelectric devicesequal in shape to one another can be constantly produced with highprecision because of the fact that the shape of the die is simplytransferred to them. The present invention makes it possible for amanufacturer to produce a piezoelectric device having a desiredthickness distribution with increased flexibility by adaptivelylaminating a plurality of sheet-like raw material elements respectivelyhaving thicknesses collectively in accordance with the desiredthickness.

In accordance with the present invention, there is provided anultrasonic probe comprising a piezoelectric device having a constructionproduced through the steps of: (c) producing a first piezoelectric bodyhaving a non-plane first surface and a plane second surface opposite tothe first surface, and a second piezoelectric body having a plane firstsurface and a plane second surface opposite to the first surface, thesecond piezoelectric body having electrodes respectively on the firstand second surfaces; and

-   -   (d) fixedly connecting the first piezoelectric body to the        second piezoelectric body with the second surface of the first        piezoelectric body held in contact with the first surface of the        second piezoelectric body. The present invention makes it        possible for a manufacturer to produce a piezoelectric device        having a predetermined uneven thickness distribution with ease,        while eliminating the need of carrying out any        technically-difficult minute machining processing such as for        example a grinding processing, thereby resulting in the fact the        piezoelectric device is kept from being excessively distorted so        that the piezoelectric device is not cracked. In addition, the        present invention makes it possible for a manufacturer to        constantly produce a plurality of piezoelectric devices equal in        shape to one another with high precision because of the fact        that the shape of the die is simply transferred to them, thereby        resulting in the fact the piezoelectric device thus produced can        reliably operate without being influenced by differences among        piezoelectric devices. The piezoelectric device having        electrodes spaced apart from each other at a constant distance        although the piezoelectric device has an uneven thickness        distribution can maintain its polarization state constant,        thereby ensuring that ultrasonic waves are transmitted and        received with high reliability.

In accordance with the present invention, there is provided anultrasonic diagnostic apparatus equipped with an ultrasonic probecomprising a piezoelectric device having a construction produced throughthe steps of: (c) producing a first piezoelectric body having anon-plane first surface and a plane second surface opposite to the firstsurface, and a second piezoelectric body having a plane first surfaceand a plane second surface opposite to the first surface, the secondpiezoelectric body having electrodes respectively on the first andsecond surfaces; and (d) fixedly connecting the first piezoelectric bodyto the second piezoelectric body with the second surface of the firstpiezoelectric body held in contact with the first surface of the secondpiezoelectric body. The ultrasonic probe thus constructed has anadvantage of stably operating without being influenced by differencesamong piezoelectric devices. The ultrasonic diagnostic apparatus thusconstructed can carry out an ultrasound diagnosis with high reliability,taking the advantage of the ultrasonic probe.

In accordance with the present invention, there is provided anondestructive testing apparatus equipped with an ultrasonic probecomprising a piezoelectric device having a construction produced throughthe steps of: (c) producing a first piezoelectric body having anon-plane first surface and a plane second surface opposite to the firstsurface, and a second piezoelectric body having a plane first surfaceand a plane second surface opposite to the first surface, the secondpiezoelectric body having electrodes respectively on the first andsecond surfaces; and (d) fixedly connecting the first piezoelectric bodyto the second piezoelectric body with the second surface of the firstpiezoelectric body held in contact with the first surface of the secondpiezoelectric body. The ultrasonic probe thus constructed has anadvantage of stably operating without being influenced by differencesamong piezoelectric devices. The nondestructive testing apparatus thusconstructed can carry out a nondestructive test with high reliability,taking the advantage of the ultrasonic probe.

BRIEF DESCRIPTION OF THE DRAWINGS

The features and advantages of a method of producing a piezoelectricdevice, a piezoelectric device, an ultrasonic probe, an ultrasonicdiagnostic apparatus, and a nondestructive testing device according tothe present invention will be more clearly understood from the followingdetailed description when considered in connection with the accompanyingdrawings.

FIG. 1 is a diagram explaining a first preferred embodiment of a methodof producing a piezoelectric device according to the present invention.

FIG. 2 is a diagram explaining another pressing process (using front,back, right, and left die walls) forming part of the first embodiment ofthe method according to the present invention.

FIG. 3 is a diagram explaining a second preferred embodiment of a methodof producing a piezoelectric device according to the present invention.

FIG. 4 is a diagram explaining another laminating process (laminating aplurality of sheet-like raw material elements equal in shape to oneanother) forming part of the second embodiment of the method accordingto the present invention.

FIG. 5 is a diagram explaining a third preferred embodiment of a methodof producing a piezoelectric device according to the present invention.

FIG. 6 is a diagram showing a piezoelectric device to which anotherembodiment of a method of producing a piezoelectric device (an edgecutting process is excluded) is applicable.

FIG. 7 is a diagram showing a piezoelectric device to which anotherembodiment of a method of producing a piezoelectric device (an edgecutting process is excluded) is applicable.

FIG. 8 is a diagram explaining another laminating process (laminating aplurality of raw material elements respectively formed with throughbores equal in shape to one another) forming part of the thirdembodiment of the method according to the present invention.

FIG. 9 is a diagram explaining a fourth preferred embodiment of a methodof producing a piezoelectric device according to the present invention.

FIG. 10 is a diagram explaining another pressing process (pressingforces are imparted in vertical, lateral, and longitudinal pressingdirections) forming part of the fourth embodiment of the methodaccording to the present invention.

FIG. 11 is a diagram explaining another laminating process (laminating aplurality of sheet-like raw material elements different in width fromone another along a width direction) forming part of the fourthembodiment of the method according to the present invention.

FIG. 12 is a schematic block diagram showing a fifth preferredembodiment of a piezoelectric device according to the present invention.

FIG. 13 is a diagram explaining a fifth preferred embodiment of a methodof producing a piezoelectric device according to the present invention.

FIG. 14 is a diagram explaining a sixth preferred embodiment of a methodof producing a piezoelectric device according to the present invention.

FIG. 15 is a diagram explaining a seventh preferred embodiment of amethod of producing a piezoelectric device according to the presentinvention.

FIG. 16 is a diagram explaining another laminating process (laminating aplurality of raw material elements equal in shape to one another for athick portion) forming part of the seventh embodiment of the methodaccording to the present invention.

FIG. 17 is a diagram explaining an eighth preferred embodiment of amethod of producing a piezoelectric device according to the presentinvention.

FIG. 18 is a diagram explaining another laminating process (laminating aplurality of raw material elements respectively formed with throughbores equal in shape to one another) forming part of the eighthembodiment of the method according to the present invention.

FIG. 19 is a schematic diagram showing another eighth embodiment of thepiezoelectric device (having a plurality of internal electrodesconstituted by two layers) according to the present invention.

FIG. 20 is a schematic block diagram showing a ninth preferredembodiment of an ultrasonic probe according to the present invention.

FIG. 21 is a schematic block diagram showing a tenth preferredembodiment of an ultrasonic probe according to the present invention.

FIG. 22 is a schematic block diagram showing an eleventh preferredembodiment of an ultrasonic diagnostic apparatus according to thepresent invention.

FIG. 23 is a schematic block diagram showing a twelfth preferredembodiment of a nondestructive testing apparatus according to thepresent invention.

FIG. 24 is a schematic block diagram showing a conventional ultrasonicprobe.

FIG. 25 is a diagram showing a method of producing a conventionalpiezoelectric device available for a conventional ultrasonic probe.

FIG. 26 is a diagram showing another method of producing a conventionalpiezoelectric device available for a conventional ultrasonic probe.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described indetail in accordance with the accompanying drawings.

[First Embodiment]

Referring now to FIG. 1 of the drawings, there is shown a firstpreferred embodiment of a method of producing a piezoelectric device 1,comprising: molding and laminating processes (first step (a)) of moldingone or more raw material elements 6 including at least one piezoelectricmaterial to form a predetermined piezoelectric element 7 (rawpiezoelectric element); and a pressing process (second step (b))imparting pressing forces to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a predetermined shape.

The present embodiment of the piezoelectric device 1 has a plane firstsurface and a concave second surface opposite to the first surface. Thesecond surface has a thickness concavely curved in a manner that thethickness of the second surface gradually increases from a centerportion toward end portions. The piezoelectric device 1 in partconstitutes an ultrasonic probe (shown FIG. 20) to be used for anultrasonic diagnostic apparatus (shown in FIG. 22) or a nondestructivetesting device (shown in FIG. 23).

A process of producing a piezoelectric device 1 comprises: a moldingprocess of molding raw materials such as for example piezoelectricceramic powders to form a plurality of sheet-like raw material elements6 (not shown in FIG. 1), a laminating process of laminating a pluralityof sheet-like raw material elements 6 to form a piezoelectric element 7(shown in FIGS. 1(a) and 1(b)), a pressing process of imparting pressingforces using a die 8 to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a predetermined shape to obtain apiezoelectric element 7 a (shown in FIGS. 1(c) and 1(d)), and a burningprocess of burning the piezoelectric element 7 a (shown in FIG. 1(e)).

As shown in FIG. 1, the raw material elements 6 are flexible and capableof being deformed when a pressing force is imparted to the raw materialelements 6. The die 8 is made of a metal material such as for exampleiron and/or the like, and has a predetermined shape so that the shape ofthe die 8 is transferred to the piezoelectric element 7. In the pressingprocess, the die 8 is used to impart pressing forces to thepiezoelectric element 7 constituted by a plurality of laminatedsheet-like raw material elements 6 to have the piezoelectric element 7molded into a piezoelectric element 7 a having a predetermined uneventhickness distribution. The piezoelectric element 7 a is shrunken afterthe burning process. This means that the shape of the die 8 is designedso that the piezoelectric element 7 is molded to form a piezoelectricdevice 1 having a predetermined uneven thickness distribution in view ofa shrinkage caused by the burning process.

In the molding process, raw materials including piezoelectric ceramicpowders such as for example PZT powders are mixed with a binding agent(including a plasticizer, if required) and immersed in a solvent. Aplurality of raw material elements are then extracted from the solventby way of, for example, a Doctor Blade technique to form a plurality ofsheet-like raw material elements 6 each having a thickness in a range ofa few ten microns to a few hundred microns.

In the laminating process, one or more sheet-like raw material elements6 as shown in FIG. 1(a) are laminated to form a piezoelectric element 7as shown in FIG. 1(b). Here, the number and the thickness of sheet-likeraw material elements 6 to be laminated are calculated in accordancewith the thickness distribution of the piezoelectric device 1 in view ofa shrinkage caused by the burning process so as to obtain apiezoelectric device 1 having a predetermined thickness distributionafter the burning process. While being laminated, the sheet-like rawmaterial elements 6 may be pressed and heated if required.

In the pressing process, the shape and the thickness distribution of thedie 8 can be transferred to the piezoelectric element 7. In the presentinvention, the die 8 made of a metal material such as for example ironand/or the like is used to impart pressing forces to the piezoelectricelement 7 in thickness directions as shown in FIG. 1(c) to have thepiezoelectric element 7 molded into a piezoelectric element 7 a having apredetermined uneven thickness distribution as shown in FIG. 1(d).

In the burning process, the piezoelectric element 7 a is not processedby any machining means such as for example grinding means, but burned toproduce a piezoelectric device 1 having a predetermined uneven thicknessdistribution. In this manner, a plurality of piezoelectric devices canbe constantly produced with high precision because of the fact that theshape of the die 8 is simply transferred to them.

As will be seen from the foregoing description, it is to be understoodthat the present embodiment of the method of producing a piezoelectricdevice according to the present invention, comprising molding andlaminating processes of molding one or more raw material elements 6including at least one piezoelectric material to form a predeterminedpiezoelectric element 7; and a pressing process of imparting pressingforces to the piezoelectric element 7 to have the piezoelectric element7 molded into a predetermined shape can produce a piezoelectric devicehaving a predetermined thickness distribution without carrying out anytechnically-difficult machining processing such as for example agrinding processing. This means that the present embodiment of themethod of producing a piezoelectric device, comprising a process oflaminating a plurality of sheet-like raw material elements 6 each havingan extremely thin thickness to form a piezoelectric element 7 canadaptively produce a piezoelectric device 1 having any thickness bycalculating the number of sheet-like raw material elements 6 to belaminated in accordance with the thickness of the piezoelectric device 1in advance. Furthermore, a plurality of piezoelectric devices equal inshape to one another can be constantly produced with high precision bythe reason that the shape of the die 8 is transferred to them.

The first embodiment of the piezoelectric device 1 thus producedcomprises a piezoelectric element 7 having one or more raw materialelements 6 including a piezoelectric material, in which pressing forceshave been imparted to the piezoelectric element 7 to have thepiezoelectric element 7 molded. The present embodiment makes it possiblefor a manufacturer to produce a piezoelectric device having a thicknessdistribution with ease and high precision.

Though it has been described in the present embodiment that theproducing method comprises a laminating process of laminating aplurality of sheet-like raw material elements 6 to produce apiezoelectric element 7, the same effect can still be obtained even whenonly one raw material element 6 is used as long as the raw materialelement 6 has a thickness approximately corresponding to the thicknessof the piezoelectric device 1. In such a case, a laborious work oflaminating a plurality of raw material elements 6 to produce apiezoelectric element 7 can be eliminated.

Though it has been described in the present embodiment that thepiezoelectric device 1 thus produced has a concave surface having athickness concavely curved in a manner that the thickness of the surfacegradually increases from a center portion toward end portions, the sameeffect can still be obtained even when the surface of the piezoelectricdevice has an arbitrary shape such as for example a convex surface,convexo-concave surface, or the like, by adaptively modifying the shapeof the die 8 in accordance with the desired shape of the surface of thepiezoelectric device.

Furthermore, though it has been described in the present embodiment thatthe piezoelectric device 1 thus produced is in the form of aquadrilateral sheet shape, the same effect can still be obtained evenwhen the piezoelectric device is in the form of an arbitrary shape suchas, for example, a disc sheet shape, by adaptively modifying the shapesof the raw material elements 6 and the die 8 in accordance with thedesired shape of the piezoelectric device.

Furthermore, while it has been described in the present embodiment thatpressing forces are imparted to the piezoelectric element 7 in pressingdirections without holding the piezoelectric element 7 with respect todirections perpendicular to the pressing directions as shown in FIG.1(c), the same effect can still be obtained even when pressing forcesare imparted to the piezoelectric element 7 in pressing directions whileholding the piezoelectric element 7 with a die wall 9 made of a metalmaterial such as for example iron and/or the like, and extending infront, back, right, and left directions perpendicular relationship tothe pressing directions as shown in FIG. 2. In such a case, thepiezoelectric element 7 is prevented from being excessively spread inthe front, back, right, and left directions perpendicular to thepressing directions during the pressing process.

[Second Embodiment]

Referring then to FIG. 3 of the drawings, there is shown a secondpreferred embodiment of a method of producing a piezoelectric device 1.The present embodiment of the producing method is different from thefirst embodiment of the producing method in the fact that the moldingand laminating process (first step (a)) further has a process oflaminating a plurality of raw material elements 6 (sheet-like rawmaterial elements) respectively having thicknesses collectively inaccordance with a thickness distribution of the piezoelectric device.Preferably, the shape and the number of sheet-like raw material elements6 to be laminated should be calculated in accordance with the thicknessdistribution of the piezoelectric device 1. The present embodiment ofthe producing method has an additional effect of being capable ofproducing a piezoelectric device 1 having a predetermined thicknessdistribution with increased flexibility by adaptively laminating aplurality of raw material elements 6 respectively having thicknessescollectively in accordance with the thickness distribution of thepiezoelectric device.

The present embodiment of the piezoelectric device 1 has a plane firstsurface and a concave second surface opposite to the first surface. Thesecond surface has a thickness concavely curved in a manner that thethickness of the second surface gradually increases from a centerportion toward end portions. The piezoelectric device 1 in partconstitutes an ultrasonic probe (shown FIG. 20) to be used for anultrasonic diagnostic apparatus (shown in FIG. 22) or a nondestructivetesting device (shown in FIG. 23).

Similar to the first embodiment of the producing process, in the presentembodiment, a process of producing a piezoelectric device 1 comprises: amolding process of molding raw materials such as for examplepiezoelectric ceramic powders to form a plurality of sheet-like rawmaterial elements 6 (not shown in FIG. 3), a laminating process oflaminating a plurality of sheet-like raw material elements 6 to form apiezoelectric element 7 (shown in FIGS. 3(a) and 3(b)), a pressingprocess of imparting pressing forces using a die 8 to the piezoelectricelement 7 to have the piezoelectric element 7 molded into apredetermined shape (shown in FIGS. 3(c) and 3(d)), and a burningprocess of burning the piezoelectric element 7 a (shown in FIG. 3(e)).

As shown in FIG. 3, the raw material elements 6, made of a piezoelectricmaterial, a binding agent, and the like, are flexible and capable ofbeing deformed when pressing forces are imparted to the raw materialelements 6, as described hereinearlier. The die 8 is made of a metalmaterial such as for example iron and/or the like, and has apredetermined shape so that the shape of the die 8 is transferred to thepiezoelectric element 7. In the pressing process, the die 8 is used toimpart pressing forces to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a piezoelectric element 7 a having apredetermined uneven thickness distribution. The shape of the die 8 isdesigned so that the piezoelectric element 7 is molded to form apiezoelectric device 1 having a predetermined uneven thicknessdistribution in view of a shrinkage caused by the burning process.

In the molding process, raw materials including piezoelectric ceramicpowders such as for example PZT powders are mixed with a binding agent(including a plasticizer, if required) and immersed in a solvent. Aplurality of raw material elements are then extracted from the solventby way of, for example, a Doctor Blade technique to form a plurality ofsheet-like raw material elements 6 each having a thickness in a range ofa few ten microns to a few hundred microns, and a unique width, ifrequired.

In the laminating process, one or more sheet-like raw material elements6 as shown in FIG. 3(a) are laminated to form a piezoelectric element 7as shown in FIG. 3(b). Here, the number and the thicknesses ofsheet-like raw material elements 6 to be laminated are calculated inaccordance with the thickness distribution of the piezoelectric device 1in view of a shrinkage caused by the burning process so as to obtain apiezoelectric device 1 having a predetermined thickness distributionafter the burning process. Furthermore, one or more sheet-like rawmaterial elements 6 respectively having shapes collectivelycorresponding to the thickness distribution of the piezoelectric deviceare laminated. For example, one or more sheet-like raw material elements6 respectively having widths collectively corresponding to the thicknessdistribution of the piezoelectric device may be laminated.Alternatively, the number of sheet-like raw material elements 6 may belaminated in accordance with the thickness distribution of thepiezoelectric device. In the present embodiment, in order to produce apiezoelectric device 1 having a thickness concavely curved in a mannerthat the thickness of the piezoelectric device gradually increases froma center portion toward end portions, a plurality of sheet-like rawmaterial elements 6 are laminated in a manner that the widths of thesheet-like raw material elements 6 decreases from a low layer toward atop layer on the both end portions. Similar to the first embodiment ofthe producing process, while being laminated, the sheet-like rawmaterial elements 6 may be pressed and heated if required.

In the pressing process, similar to the first embodiment of theproducing process, a die 8 made of a metal material such as for exampleiron and/or the like is used to impart pressing forces to thepiezoelectric element 7 in thickness directions as shown in FIG. 3(c) tohave the piezoelectric element 7 molded into a piezoelectric element 7 ahaving a predetermined uneven thickness distribution as shown in FIG.3(d). The present embodiment of the producing method can restrict thepressing forces imparted by the die 8 to the piezoelectric element 7 toa certain degree, prevent the piezoelectric element 7 from beingunnecessarily and abnormally deformed, and reduce a residual stressremaining in the piezoelectric element 7 a by the reason that thepiezoelectric element 7 laminated in the previous laminating process hasa shape approximately similar to the thickness distribution of thepiezoelectric device 1 as shown in FIG. 3(b). Furthermore, the presentembodiment of the producing method can advantageously produce apiezoelectric device whose thickness distribution is so large (thedifference between its thin portion and thick portion is extremelylarge) that the thickness distribution cannot be formed by simplydeforming the piezoelectric element 7.

In the burning process, similar to the first embodiment of the producingprocess, the piezoelectric element 7 a is not processed by any machiningmeans such as for example grinding means, but burned to produce apiezoelectric device 1 having a predetermined uneven thicknessdistribution. In this manner, a plurality of piezoelectric devices canbe constantly produced with high precision because of the fact that theshape of the die 8 is simply transferred to them. The same effect canstill be obtained even when only one raw material element 6 is used. Insuch a case, a laborious work of laminating a plurality of raw materialelements 6 to produce a piezoelectric element 7 can be eliminated.

As will be seen from the foregoing description, it is to be understoodthat the present embodiment of the piezoelectric device 1 according tothe present invention, comprising a piezoelectric element 7 a (rawpiezoelectric element) including one or more raw material elements 6(sheet-like raw material elements) respectively having shapes laminatedin accordance with a thickness distribution of the piezoelectric device,for example, widths collectively corresponding to the thicknessdistribution of the piezoelectric device to form a piezoelectric element7 a can produce a piezoelectric device having a desired thicknessdistribution with high precision. This means that the present embodimentof the producing method comprising a process of laminating a pluralityof sheet-like raw material elements 6 each having an extremely thinthickness to form a piezoelectric element 7 can adaptively produce apiezoelectric device 1 having any thickness distribution by calculatingthe number of sheet-like raw material elements 6 to be laminated inaccordance with the thickness distribution of the piezoelectric device 1in advance.

Though it has been described in the present embodiment that thepiezoelectric device 1 thus produced has a concave surface having athickness concavely curved in a manner that the thickness of the surfacegradually increases from a center portion toward end portions, the sameeffect can still be obtained even when the surface of the piezoelectricdevice has an arbitrary shape such as for example a convex surface,convexo-concave surface, or the like, by selectively increasing thenumber of the raw material elements 6 to be laminated for a thickportion without restricting the shape of the piezoelectric device 1.

Furthermore, though it has been described in the present embodiment thatthe piezoelectric device 1 thus produced is in the form of aquadrilateral sheet shape, the same effect can still be obtained evenwhen the piezoelectric device is in the form of an arbitrary shape suchas, for example, a disc sheet shape, by adaptively modifying the shapesof the raw material elements 6 and the die 8 in accordance with thedesired shape of the piezoelectric device.

Furthermore, while it has been described in the present embodiment thata plurality of raw material elements 6 are laminated to produce apiezoelectric device 1 in a manner that the widths of the raw materialelements 6 decreases from a low layer toward a top layer on the both endportions, the same effect can still be obtained even when a plurality ofraw material elements 6 equal in width or shape to one another arelaminated on the both ends to produce a piezoelectric element 7 as shownin FIG. 4. In such a case, a laborious work of carefully laminating theraw material elements 6 in accordance with their widths is eliminated,and the shapes of the raw material elements 6 to be laminated are notrestricted by the reason that the number of the raw material elements 6to be laminated can be selectively increased for a thick portion.

[Third Embodiment]

Referring then to FIG. 5 of the drawings, there is shown a thirdpreferred embodiment of a method of producing a piezoelectric device 1.The present embodiment of the producing method is different from thefirst embodiment of the producing method in the fact that the moldingand laminating process (first step (a)) further has a process oflaminating one or more raw material elements respectively formed withthrough bores in accordance with a thickness distribution of thepiezoelectric device 1. The present embodiment of the producing methodhas an additional effect of being capable of producing a piezoelectricdevice 1 having a predetermined shape and thickness distribution withincreased flexibility.

The present embodiment of the piezoelectric device 1 has a plane firstsurface and a concave second surface opposite to the first surface. Thesecond surface has a thickness concavely curved in a manner that thethickness of the second surface gradually increases from a centerportion toward end portions. The piezoelectric device 1 in partconstitutes an ultrasonic probe (shown FIG. 20) to be used for anultrasonic diagnostic apparatus (shown in FIG. 22) or a nondestructivetesting device (shown in FIG. 23).

Similar to the first embodiment of the producing process, in the presentembodiment, a process of producing a piezoelectric device 1 comprises: amolding process of molding raw materials such as for examplepiezoelectric ceramic powders to form a plurality of sheet-like rawmaterial elements (not shown in FIG. 5), a die-cutting process ofdie-cutting the sheet-like raw material elements, as many as required,to obtain a plurality of window frame-like raw material elements 6respectively formed with through bores in the form of rectangular windowshapes (not shown in FIG. 5), a laminating process of laminating aplurality of window frame-like raw material elements 6 and a pluralityof sheet-like raw material elements 6 to form a piezoelectric element 7A(shown in FIGS. 5(a) and 5(b)), an edge cutting process of cutting offthe front end rear edges of the piezoelectric element 7A (shown in FIG.5(c)) to obtain a piezoelectric element 7, a pressing process ofimparting pressing forces using a die 8 to the piezoelectric element 7to have the piezoelectric element 7 molded into a predetermined shape toobtain a piezoelectric element 7 a (shown in FIGS. 5(d) and 5(e)), and aburning process of burning the piezoelectric element 7 a (shown in FIG.5(f)).

As shown in FIG. 5, the raw material elements 6, made of a piezoelectricmaterial, a binding agent, and the like, are flexible and capable ofbeing deformed when pressing forces are imparted to the raw materialelements 6, as described hereinearlier. The die 8 is made of a metalmaterial such as for example iron and/or the like, and has apredetermined shape so that the shape of the die 8 is transferred to thepiezoelectric element 7. In the pressing process, the die 8 is used toimpart pressing forces to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a piezoelectric element 7 a having apredetermined uneven thickness distribution. The shape of the die 8 isdesigned so that the piezoelectric element 7 is molded to form apiezoelectric device 1 having a predetermined uneven thicknessdistribution in view of a shrinkage caused by the burning process.

In the molding process, raw materials including piezoelectric ceramicpowders such as for example PZT powders are mixed with a binding agent(including a plasticizer, if required) and immersed in a solvent. Aplurality of raw material elements are then extracted from the solventby way of, for example, a Doctor Blade technique to form a plurality ofsheet-like raw material elements each having a thickness in a range of afew ten microns to a few hundred microns.

In the die-cutting process, the sheet-like raw material elements, asmany as required, are die-cut to obtain a plurality of window frame-likeraw material elements 6 respectively formed with through bores differentin shape and size.

In the laminating process, one or more sheet-like raw material elements6 including window frame-like raw material elements 6 as shown in FIG.5(a) are laminated to form a piezoelectric element 7A as shown in FIG.5(b). Here, the number and the thicknesses of sheet-like raw materialelements 6 to be laminated are calculated in accordance with thethickness distribution of the piezoelectric device 1 in view of ashrinkage caused by the burning process so as to obtain a piezoelectricdevice 1 having a predetermined thickness distribution after the burningprocess. In the present embodiment, the piezoelectric device 1 to beproduced has a thickness concavely curved in a manner that the thicknessof the piezoelectric device 1 gradually increases from a center portiontoward end portions along the minor axis. In accordance with thethickness distribution of the piezoelectric device 1 to be produced, oneor more sheet-like raw material elements 6 respectively formed withthrough-bores are laminated. Preferably, the through bores of the one ormore sheet-like raw material elements 6 to be laminated should be insize collectively in accordance with the thickness distribution of thepiezoelectric device 1. More specifically, a plurality of windowframe-like raw material elements 6 are laminated in a manner that thewidths of the window frame-like raw material elements 6 graduallydecreases, i.e., the size of each of the through bores of the windowframe-like raw material elements 6 gradually increases from a low layertoward a top layer on the both end portions as shown in FIG. 5(b).Similar to the first embodiment of the producing process, while beinglaminated, the sheet-like raw material elements 6 may be pressed andheated if required.

Each of the raw material elements 6 has an outer edge. Preferably, theraw material elements 6 may be made in a manner that the outer edges ofthe raw material elements 6 are equal in shape (size) to one another andthe window frame-like raw material elements 6 have through boresaccurately die-cut with respect to their outer edges so that the rawmaterial elements 6 can be easily laminated without displacements simplyafter positioning the raw material elements 6 with respect to theirrespective outer edges. Alternatively, each of the raw material elements6 may have at least one perpendicular edge in a manner that the rawmaterial elements 6 have through bores accurately die-cut with respectto their perpendicular edges so that the raw material elements 6 can beeasily laminated without displacements simply after positioning theperpendicular edges of the raw material elements 6 although the rawmaterial elements 6 are not equal in shape to one another. Furthermore,the raw material elements 6 may be made in a manner that the throughbores of the raw material elements 6 in size collectively correspond tothe thickness distribution of the piezoelectric device 1 along a widthdirection (in the present embodiment, the raw material elements 6 arelaminated in a manner that the size of each of the through bores of theraw material elements 6 gradually increases along the width directionfrom the lower layer to the top layer) so as to form the piezoelectricelement 7A having a thickness concavely curved in a manner that thethickness of the piezoelectric element 7A gradually increases from acenter portion toward end portions along the minor axis.

In the edge cutting process, unwanted parts of the piezoelectric element7A collectively constituted by the raw material elements 6 are cut off.The unwanted parts of the piezoelectric element 7A may not be cut offbut used as reinforcing parts in the case that the piezoelectric element7A has such an extremely thin portion that the piezoelectric element 7Aas a whole would be abnormally curved and fail to lose its shape whenthe unwanted parts of the piezoelectric element 7A are cut off. In thiscase, the unwanted parts of the piezoelectric element 7A may be cut offafter the pressing process or the burning process.

In the pressing process, similar to the first embodiment of theproducing process, a die 8 made of a metal material such as for exampleiron and/or the like is used to impart pressing forces to thepiezoelectric element 7 in thickness directions as shown in FIG. 5(d) tohave the piezoelectric element 7 molded into a piezoelectric element 7 ahaving a predetermined uneven thickness distribution as shown in FIG.5(e). In the present embodiment of the producing method, the pressingforces imparted by the die 8 to the piezoelectric element 7 isrestricted to a certain degree, the piezoelectric element 7 is preventedfrom being unnecessarily and abnormally deformed, and a residual stressremaining in the piezoelectric element 7 a is reduced by the reason thatthe piezoelectric element 7 laminated in the previous laminating processhas a shape approximately similar to the thickness distribution of thepiezoelectric device 1 as shown in FIG. 5(c). Furthermore, the presentembodiment of the producing method can advantageously produce apiezoelectric device whose thickness distribution is so large (thedifference between its thin portion and thick portion is extremelylarge) that the thickness distribution cannot be formed by simplydeforming the piezoelectric element 7.

In the burning process, similar to the first embodiment of the producingprocess, the piezoelectric element 7 a is not processed by any machiningmeans such as for example grinding means, but burned to produce apiezoelectric device 1 having a predetermined uneven thicknessdistribution. In this manner, a plurality of piezoelectric devices canbe constantly produced with high precision because of the fact that theshape of the die 8 is simply transferred to them.

As will be seen from the foregoing description, it is to be understoodthat the present embodiment of the piezoelectric device 1 according tothe present invention, comprising a piezoelectric element 7 a (rawpiezoelectric element) including one or more raw material elements 6(sheet-like raw material element) respectively formed with through boresin accordance with a thickness distribution of the piezoelectric devicecan produce a piezoelectric device having a desired thicknessdistribution with high precision.

Furthermore, the present embodiment of the producing method comprising aprocess of laminating a plurality of raw material elements 6respectively formed with through bores in accordance with a thicknessdistribution of the piezoelectric device can adaptively produce apiezoelectric device 1 having any shape and thickness distribution.

Though it has been described in the present embodiment that thepiezoelectric device 1 thus produced has a concave surface having athickness concavely curved in a manner that the thickness of the surfacegradually increases from a center portion toward end portions, the sameeffect can still be obtained even when the surface of the piezoelectricdevice has an arbitrary shape such as for example a convex surface,convexo-concave surface, or the like, by selectively increasing thenumber of the raw material elements 6 to be laminated for a thickportion 1 in view of the positions, the sizes, and the number of theirthrough bores without restricting the shape of the piezoelectric device.

Furthermore, though it has been described in the present embodiment thatthe unwanted parts of the piezoelectric element 7A are cut off by thereason that the piezoelectric device 1 thus produced should have aconcave surface having a thickness concavely curved in a manner that thethickness of the surface gradually increases from a center portiontoward end portions (two directions), the same effect can still beobtained even when the piezoelectric device 1 thus produced has aconcave surface having a thickness concavely curved in a manner that thethickness of the surface gradually increases from a center portiontoward end portions as shown in FIGS. 6(a) and 6(b) or FIGS. 7(a) and7(b). In such a case, the piezoelectric element 7A has no unwanted partsto be cut off, and the edge cutting process is accordingly eliminated.

Furthermore, while it has been described in the present embodiment thata plurality of raw material elements 6 are laminated to obtain apiezoelectric element 7A similar in shape to the piezoelectric device 1to be produced in a manner that the widths of through bores of the rawmaterial elements 6 increases from a low layer toward a top layer, thesame effect can still be obtained even when a plurality of raw materialelements 6 respectively having through bores equal in width or shape toone another as shown in FIG. 8(a) are laminated to produce apiezoelectric element 7A as shown in FIG. 8(b) as long as thepiezoelectric element 7A is similar in shape to the piezoelectric device1 to be produced, and the number of the raw material elements 6 to belaminated is selectively increased for a thick portion in view of thepositions, the sizes, and the number of their through bores. In such acase, a laborious work of selectively laminating the raw materialelements 6 in accordance with the widths of their through bores iseliminated without restricting the shape of the piezoelectric device 1.

[Fourth Embodiment]

Referring then to FIG. 9 of the drawings, there is shown a fourthpreferred embodiment of a method of producing a piezoelectric device 1.The present embodiment of the producing method is different from thefirst embodiment of the producing method in the fact that pressingforces are imparted to the piezoelectric element 7 in laminatingdirections, along which the raw material elements 6 are laminated, anddirections perpendicular to the laminating directions. The presentembodiment of the producing method has an additional effect of beingcapable of producing a piezoelectric device 1 having a predetermineduneven width distribution without carrying out any technically-difficultminute machining processing.

The present embodiment of the piezoelectric device 1 has a widthconcavely curved in a manner that the width of the piezoelectric device1 gradually increases from a middle portion toward upper and lower endportions. The piezoelectric device 1 in part constitutes an ultrasonicprobe (shown FIG. 20) to be used for an ultrasonic diagnostic apparatus(shown in FIG. 22) or a nondestructive testing device (shown in FIG.23).

Similar to the first embodiment of the producing process, in the presentembodiment, a process of producing a piezoelectric device 1 comprises: amolding process of molding raw materials such as for examplepiezoelectric ceramic powders to form a plurality of sheet-like rawmaterial elements 6 (not shown in FIG. 9), a laminating process oflaminating a plurality of sheet-like raw material elements 6 to form apiezoelectric element 7 (shown in FIGS. 9(a) and 9(b)), a pressingprocess of imparting pressing forces using a die 8 in four directions tothe piezoelectric element 7 to have the piezoelectric element 7 moldedinto a predetermined shape (shown in FIG. 9(c)), and a burning processof burning the piezoelectric element 7 a (shown in FIGS. 9(d) and 9(e)).

As shown in FIG. 9, the raw material elements 6, made of a piezoelectricmaterial, a binding agent, and the like, are flexible and capable ofbeing deformed when pressing forces are imparted to the raw materialelements 6, as described hereinearlier. The die 8 is made of a metalmaterial such as for example iron and/or the like, and has apredetermined shape so that the shape of the die 8 is transferred to thepiezoelectric element 7. In the pressing process, the die 8 is used toimpart pressing forces to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a piezoelectric element 7 a having apredetermined uneven thickness distribution. The shape of the die 8 isdesigned so that the piezoelectric element 7 is molded to form apiezoelectric device 1 having a predetermined uneven thicknessdistribution in view of a shrinkage caused by the burning process.

In the molding process, raw materials including piezoelectric ceramicpowders such as for example PZT powders are mixed with a binding agent(including a plasticizer, if required) and immersed in a solvent. Aplurality of raw material elements are then extracted from the solventby way of, for example, a Doctor Blade technique to form a plurality ofsheet-like raw material elements 6 each having a thickness in a range ofa few ten microns to a few hundred microns.

In the laminating process, similar to the first embodiment of theproducing process, one or more sheet-like raw material elements 6 asshown in FIG. 9(a) are laminated to form a piezoelectric element 7 asshown in FIG. 9(b). Here, the number and the thicknesses of sheet-likeraw material elements 6 to be laminated are calculated in accordancewith the thickness distribution of the piezoelectric device 1 in view ofa shrinkage caused by the burning process so as to obtain apiezoelectric device 1 having a predetermined thickness distributionafter the burning process. While being laminated, the sheet-like rawmaterial elements 6 may be pressed and heated if required.

In the pressing process, a die 8 made of a metal material such as forexample aluminum, brass, and/or the like, having a solidity required forthe pressing process, and capable of being easily worked, is used toimpart pressing forces to the piezoelectric element 7 as shown in FIG.9(c). In the present embodiment, the die 8 has two vertical pressingsurfaces opposing to each other and to be held in pressing contact withthe piezoelectric element 7 in vertical directions and two convex-shapedlateral pressing surfaces opposing to each other and to be held inpressing contact with the piezoelectric element 7 in lateral directions.Using the die 8, pressing forces are imparted to the piezoelectricelement 7 to have the piezoelectric element 7 molded into apiezoelectric element 7 a having an uneven width distribution concavelycurved in a manner that the width of the piezoelectric element 7 agradually increases from a middle portion toward upper and lower endportions as shown in FIG. 9(d). In the present embodiment, the die 8 ismade of a metal material capable of being molded into a desired shape,and the lateral sides of the piezoelectric element 7 constituted by aplurality of thin sheet-like raw material elements 6 are not processeddirectly by any processing tool. This means that the present embodimentof the producing method can prevent the piezoelectric device 1 frombeing damaged and constantly produce a plurality of piezoelectricdevices with high precision because of the fact that the lateral sidesof the piezoelectric element 7 are not processed directly by anyprocessing tool, but held in pressing contact with the lateral pressingsurfaces of the die 8 while the pressing forces are imparted, and theshape of the die 8 is simply transferred to them.

In the burning process, the piezoelectric element 7 a is not processedby any machining means such as for example grinding means, but burned toproduce a piezoelectric device 1 having a predetermined uneven thicknessdistribution. In this manner, a plurality of piezoelectric devices canbe constantly produced with high precision because of the fact that theshape of the die 8 is simply transferred to them as described in theabove.

Though it has been described in the present embodiment that thepiezoelectric device 1 thus produced has a shape with a widthdistribution concavely curved in a manner that the width of thepiezoelectric device 1 gradually increases from a middle portion towardupper and lower end portions, the same effect can still be obtained evenwhen the piezoelectric device 1 has a shape with any width distribution,by imparting pressing forces to the piezoelectric element 7 in thelateral directions using a die 8 molded into a shape having a widthdistribution corresponding to that of the piezoelectric device 1.

Furthermore, though it has been described in the present embodiment thatthe piezoelectric device 1 thus produced has a shape with an unevenwidth distribution in lateral directions, the same effect can still beobtained even when the piezoelectric device 1 has a shape with anyuneven width distribution in longitudinal directions perpendicular tothe vertical and lateral directions, or when the piezoelectric device 1has a shape with any uneven width distribution both in the lateral andthe longitudinal directions, by adaptively imparting pressing forces tothe piezoelectric element 7 in the lateral directions or both in thelateral and the longitudinal directions using a die 8.

Furthermore, though it has been described in the present embodiment thatpressing forces are imparted to the piezoelectric element 7 using a die8 having plane pressing surfaces in the vertical directions, i.e.,thickness directions to produce a piezoelectric device 1 having a planethickness distribution, the same effect can still be obtained even whenthe piezoelectric device 1 has a shape having both an uneven widthdistribution in the lateral direction and an uneven thicknessdistribution in the vertical directions by selectively adopting a die 8having a shape in accordance with the shape of the piezoelectric device1 to be produced.

Furthermore, while it has been described in the present embodiment thatpressing forces are imparted to the piezoelectric element 7 in thevertical and lateral pressing directions without holding thepiezoelectric element 7 with respect to the longitudinal directions, thesame effect can still be obtained even when pressing forces are impartedto the piezoelectric element 7 in the vertical and lateral pressingdirections while holding the piezoelectric element 7 with a die wall 9made of a metal material such as for example aluminum, brass, and/or thelike, and extending in perpendicular relationship to the vertical andlateral pressing directions as shown in FIG. 10. In such a case, thepiezoelectric element 7 is prevented from being excessively spread inthe longitudinal directions during the pressing process.

Furthermore, though it has been described in the present embodiment thatthe producing method comprises a pressing process of imparting pressingforces in lateral directions using a die 8 to the piezoelectric element7 constituted by a plurality of laminated raw material elements 6identical in shape to one another, the same effect can still be obtainedeven when a plurality of raw material elements 6 different in lateralwidth (length in lateral direction) from one another as shown in FIG.11(a) are laminated to produce a piezoelectric element 7 approximatelysimilar in shape to the piezoelectric device 1 to be produced as shownin FIG. 11(b) before the pressing process. As will be seen from theforegoing description, it is to be understood that the producing method,which comprises a laminating process of laminating a plurality of rawmaterial elements 6 different in lateral width from one another in amanner that the lateral width of the raw material elements 6 increasesfrom a middle portion toward upper and lower end portions can adaptivelyproduce a piezoelectric device 1 having any uneven width distributionwith high precision. Further, the pressing forces imparted by the die 8to the piezoelectric element 7 are restricted to a certain degree, thepiezoelectric element 7 is prevented from being unnecessarily andabnormally deformed, and a residual stress remaining in thepiezoelectric element 7 a is reduced.

[Fifth Embodiment]

Referring to FIG. 12 of the drawings, there is shown a fifth preferredembodiment of the piezoelectric device 1 comprising a piezoelectricelement 7 (raw piezoelectric element) including a plurality of laminatedraw material elements 6 (sheet-like raw material elements), an externalelectrode 10, and an internal electrode 11 (a plurality of electrodesspaced apart from each other at a predetermined distance.

As shown in FIG. 12, the piezoelectric device 1 is made of, for example,piezoelectric ceramics, and has a thickness concavely curved in a mannerthat the thickness of the piezoelectric device 1 gradually increasesfrom a center portion toward end portions along lateral directions. Theexternal electrode 10 is formed on a plane bottom surface of thepiezoelectric device 1, and made of, for example, baking silver, goldsputter-coated material, and/or the like. The internal electrode 11 isformed on an inner surface of piezoelectric device 1, spaced apart fromand in parallel relationship to the external electrode 10. Thepiezoelectric device 1 further comprises an extension electrode 12beside the internal electrode 11 and extending from the internal surfaceto the bottom surface through a side surface of the piezoelectric device1 for ease in electrical connection. The extension electrode 12 and theexternal electrode 10 are spaced apart from each other at apredetermined distance on the bottom surface and electrically insulatedfrom each other.

In the conventional piezoelectric device, electrodes are in generalformed on an upwardly exposed upper surface and a downwardly exposedbottom surface of the piezoelectric device. In the case of theconventional piezoelectric device having such a shape as shown in FIG.12, the first electrode formed on the upper surface of the piezoelectricdevice is concavely curved and the second electrode formed on the bottomsurface is plane. This means that the distance between the first andsecond electrodes is not constant but varied in a manner that thedistance between the first and second electrodes gradually increasesfrom a center portion toward end portions. This leads to the fact thatelectric field strength applied to the piezoelectric device and thuspolarization state of the piezoelectric device become uneven along alateral direction as shown in FIG. 12 in the event that thepiezoelectric device is used and polarized. Further, the fact that theelectric field applied to the thin center portion is greater than theelectric field applied to the end portion leads to the fact that thepiezoelectric device is caused to be excessively distorted, therebymaking it easier for the piezoelectric device to be cracked(microcracked).

On the contrary, in the case of the present embodiment of thepiezoelectric device 1 as shown in FIG. 12 comprising an externalelectrode 10 and an internal electrode 11 spaced apart from each otherat a predetermined distance, electric field strength applied to thepiezoelectric device and thus polarization state of the piezoelectricdevice are constant in the event that the piezoelectric device 1 is usedand polarized by the reason that the distance between the externalelectrode and the internal electrode is constant, as well as thepiezoelectric device is kept from being excessively distorted so thatthe piezoelectric device is not cracked (microcracked).

The present embodiment of the method of producing a piezoelectric device1 will be described hereinlater with reference to FIG. 13. The presentembodiment of the piezoelectric device 1 comprises a first piezoelectricbody 1 a and a second piezoelectric body 1 b. The first piezoelectricbody 1 a has a concave upper surface and a plane lower surface oppositeto the upper surface. The second piezoelectric body 1 b has a planeupper surface and a plane lower surface opposite to the upper surface,an external electrode 10 formed on the lower surface and an internalelectrode 11 formed on the upper surface. The piezoelectric device 1further comprises an extension electrode 12 extending from the internalsurface to the lower surface through a right side surface of thepiezoelectric device 1 for ease in an electrical connection. Theextension electrode 12 and the external electrode 10 are spaced apartfrom each other at a predetermined distance on the lower surface andelectrically insulated from each other. The first piezoelectric body 1 aand the second piezoelectric body 1 b are fixedly connected with eachother with an adhesive material such as for example an epoxy adhesivematerial, a silver paste, or the like to produce a piezoelectric device1.

As will be seen from the foregoing description, it is to be understoodthat the present embodiment of the piezoelectric device 1 according tothe present invention, comprising a piezoelectric element 7 having aplurality of laminated raw material elements 6 and an external electrode10 and an internal electrode 11 spaced apart from each other at apredetermined distance can keep an electric field strength applied tothe piezoelectric device 1 constant and thus realize an evenpolarization.

Furthermore, the present embodiment of the method of producing apiezoelectric device 1, comprising a process of producing a firstpiezoelectric body 1 a having a non-plane first surface and a planesecond surface opposite to the first surface, and a second piezoelectricbody 1 b having a plane first surface and a plane second surfaceopposite to the first surface, the second piezoelectric body 1 b havingan internal electrode 11, an external electrode 10, and an extensionelectrode 12 on the first and second surfaces; and a process of fixedlyconnecting the first piezoelectric body 1 a to the second piezoelectricbody 1 b with the second surface of the first piezoelectric body 1 aheld in contact with the first surface of the second piezoelectric body1 b can keep an electric field strength applied to the piezoelectricdevice 1 constant and thus realize an even polarization. Furthermore,the present embodiment of the piezoelectric device 1 is kept from beingexcessively distorted while the piezoelectric device is used andpolarized, thereby protecting the piezoelectric device 1 from beingcracked (microcracked).

[Sixth Embodiment]

Referring then to FIG. 14 of the drawings, there is shown a sixthpreferred embodiment of a method of producing a piezoelectric device 1.The present embodiment of the producing method is different from thefifth embodiment of the producing method in the fact that at least onepiece of internal electrode 11 is intervening between at least twopieces of the raw material elements 6 made of a mixture of apiezoelectric material and a binding agent. The present embodiment ofthe producing method has additional effects of being capable ofproducing a piezoelectric device 1 having a predetermined thicknessdistribution with ease and increased flexibility as well as realizing aneven polarization, thereby protecting the piezoelectric device 1 frombeing cracked (microcracked).

Similar to the fifth embodiment, the present embodiment of thepiezoelectric device 1 has a thickness concavely curved in a manner thatthe thickness of the piezoelectric device 1 gradually increases from acenter portion toward end portions along lateral directions. Thepiezoelectric device 1 further comprises an external electrode 10 formedon a plane bottom surface of the piezoelectric device 1, an internalelectrode 11 formed inside of the piezoelectric device 1 and spacedapart from and substantially in parallel relationship to the externalelectrode 10, and an extension electrode 12 extending from the internalelectrode 11 to the bottom surface of the piezoelectric device 1 througha side surface of the piezoelectric device 1.

Similar to the first embodiment of the producing process, in the presentembodiment, a process of producing a piezoelectric device 1 comprises: amolding process of molding raw materials such as for examplepiezoelectric ceramic powders to form a plurality of sheet-like rawmaterial elements 6 (not shown in FIG. 14), a laminating process oflaminating a plurality of sheet-like raw material elements 6 (includingat least one piece of an internal electrode 11) to form a piezoelectricelement 7 (shown in FIGS. 14(a) and 14(b)), a pressing process ofimparting pressing forces to the piezoelectric element 7 in verticalpressing directions using a die 8 to have the piezoelectric element 7molded into a predetermined shape to produce a piezoelectric element 7 a(shown in FIG. 14(c)), a burning process of burning the piezoelectricelement 7 a to produce a piezoelectric device 1 (shown in FIGS. 14(d)and 14(e)), and an electrode forming process of forming an externalelectrode 10 and an extension electrode 12 for the piezoelectric device1 thus produced (shown in FIG. 14(f)).

As shown in FIG. 14, the raw material elements 6, made of apiezoelectric material, a binding agent, and the like, are flexible andcapable of being deformed when pressing forces are imparted to the rawmaterial elements 6, as described hereinearlier. The die 8 is made of ametal material such as for example iron and/or the like, and has apredetermined shape so that the shape of the die 8 is transferred to thepiezoelectric element 7. In the pressing process, the die 8 is used toimpart pressing forces to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a piezoelectric element 7 a having apredetermined uneven thickness distribution. The shape of the die 8 isdesigned so that the piezoelectric element 7 is molded to form apiezoelectric device 1 having a predetermined uneven thicknessdistribution in view of a shrinkage caused by the burning process.

In the molding process, raw materials including piezoelectric ceramicpowders such as for example PZT powders are mixed with a binding agent(including a plasticizer, if required) and immersed in a solvent. Aplurality of raw material elements are then extracted from the solventby way of, for example, a Doctor Blade technique to form a plurality ofsheet-like raw material elements 6 each having a thickness in a range ofa few ten microns to a few hundred microns.

In the laminating process, one or more sheet-like raw material elements6 are laminated to form a piezoelectric element 7. Similar to the firstembodiment of the producing process, the number and the thicknesses ofsheet-like raw material elements 6 to be laminated are calculated inaccordance with the thickness distribution of the piezoelectric device 1in view of a shrinkage caused by the burning process so as to obtain apiezoelectric device 1 having a predetermined thickness distributionafter the burning process. On a surface of the sheet-like raw materialelement 6, an internal electrode 11 made of an electrode material suchas, for example, platinum paste capable of resisting high temperaturesduring the burning process is formed (shown in FIG. 14(a)). The positionof the sheet-like raw material element 6 having the internal electrode11 should be determined so that the internal electrode 11 is placed at apredetermined position of the piezoelectric device 1 with respect to thethickness direction after the burning process. Further, the position andthe size of the internal electrode 11 on the surface of the sheet-likeraw material element 6 should be determined so that the internalelectrode 11 could be electrically connected with a signal wire, notshown in FIG. 14, to receive an electric signal therefrom. In FIG. 14,the internal electrode 11 is placed a little to the right side of thesheet-like raw material element 6 and not protruded from the left sideof the sheet-like raw material element 6 so that the internal electrode11 is connected with the signal wire on the right side of thepiezoelectric device 1, and unexpected problem such as a short circuitwould not occur on the left side of the piezoelectric device 1.

In the pressing process, a die 8 made of a metal material such as forexample aluminum, brass, and/or the like, having a solidity required forthe pressing process, and capable of being easily worked, is used toimpart pressing forces to the piezoelectric element 7 as shown in FIG.14(c). In the present embodiment, the die 8 has two vertical pressingsurfaces opposing to each other and to be held in pressing contact withthe piezoelectric element 7 in vertical directions. Using the die 8,pressing forces are imparted to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a piezoelectric element 7 a havingan uneven thickness distribution concavely curved in a manner that thethickness of the piezoelectric element 7 a gradually increases from acenter portion toward end portions, and an internal electrode 11 spacedapart from and substantially in parallel relationship to the bottomsurface as shown in FIG. 14(d). As will be seen from the foregoingdescription, the present embodiment of the producing method, in whichthe die 8 is made of a metal material capable of being molded into adesired shape, and the vertical sides of the piezoelectric element 7 areheld in pressing contact with the vertical pressing surfaces of the die8 while the pressing forces are imparted so that the shape of the die 8is simply transferred to them can prevent the piezoelectric device 1from being damaged as well as constantly produce a plurality ofpiezoelectric devices with high precision.

In the burning process, the piezoelectric element 7 a is not processedby any machining means such as for example grinding means, but burned toproduce a piezoelectric device 1 having a predetermined uneven thicknessdistribution. In this manner, a plurality of piezoelectric devices canbe constantly produced with high precision because of the fact that theshape of the die 8 is simply transferred to them.

In the electrode forming process, an external electrode 10 made of, forexample, baking silver, gold sputter-coated material, and/or the like,is formed on a plane bottom surface of the piezoelectric device 1 afterthe burning process as shown in FIG. 14(f). Further, an extensionelectrode 12 is formed for ease in electrical connection with theinternal electrode 11. The extension electrode 12 is electricallyconnected with the internal electrode 11 on the right side surface ofthe piezoelectric device 1A, and extending therefrom to the bottomsurface along the right side surface of the piezoelectric device 1. Theextension electrode 12 is made of an electrode material such as, forexample, baking silver, gold sputter-coated material, and/or the like,on the piezoelectric device 1 having a desired shape.

Though it has been described in the present embodiment that thepiezoelectric device 1A thus produced has a concave surface having athickness concavely curved in a manner that the thickness of the surfacegradually increases from a center portion toward end portions, the sameeffect can still be obtained even when the surface of the piezoelectricdevice 1A has an arbitrary shape such as for example a convex surface,convexo-concave surface, or the like, by adaptively modifying the shapeof the die 8 in accordance with the desired shape of the surface of thepiezoelectric device without restricting the shape of the piezoelectricdevice 1A.

Furthermore, though it has been described in the present embodiment thatthe piezoelectric device 1 thus produced is in the form of aquadrilateral sheet shape, the same effect can still be obtained evenwhen the piezoelectric device is in the form of an arbitrary shape suchas, for example, a disc sheet shape, by adaptively modifying the shapesof the raw material elements 6 and the die 8 in accordance with thedesired shape of the piezoelectric device.

Furthermore, while it has been described in the present embodiment thatpressing forces are imparted to the piezoelectric element 7 in verticalpressing directions, the same effect can still be obtained even whenpressing forces are imparted to the piezoelectric element 7 in thevertical pressing directions while holding the piezoelectric element 7with a die wall 9 (shown in FIG. 2) so that the piezoelectric element 7is prevented from being excessively spread in the directionsperpendicular to the pressing directions during the pressing process.

[Seventh Embodiment]

Referring then to FIG. 15 of the drawings, there is shown a seventhpreferred embodiment of a method of producing a piezoelectric device 1.The present embodiment of the producing method is different from thesixth embodiment of the producing method in the fact that at least onepiece of internal electrode 11 is intervening between at least twopieces of the raw material elements 6 made of a mixture of apiezoelectric material and a binding agent, wherein the raw materialelements 6 are laminated in a manner that the number of the laminatedraw material elements 6 selectively increases for a thick portion of thepiezoelectric device 1A. The present embodiment of the producing methodhas additional effects of being capable of producing a piezoelectricdevice 1 having a predetermined thickness distribution with ease andincreased flexibility by selectively increasing the number of the rawmaterial elements 6 to be laminated for a thick portion as well asrealizing an even polarization, thereby protecting the piezoelectricdevice 1 from being cracked.

Similar to the fifth embodiment, the present embodiment of thepiezoelectric device 1 has a thickness concavely curved in a manner thatthe thickness of the piezoelectric device 1 gradually increases from acenter portion toward end portions along lateral directions. Thepiezoelectric device 1 further comprises an external electrode 10 formedon a plane bottom surface of the piezoelectric device 1, an internalelectrode 11 formed inside of the piezoelectric device 1 and spacedapart from and substantially in parallel relationship to the externalelectrode 10, and an extension electrode 12 extending from the internalelectrode 11 to the bottom surface of the piezoelectric device 1 througha side surface of the piezoelectric device 1.

Similar to the first embodiment of the producing process, in the presentembodiment, a process of producing a piezoelectric device 1 comprises: amolding process of molding raw materials such as for examplepiezoelectric ceramic powders to form a plurality of sheet-like rawmaterial elements 6 (not shown in FIG. 15), a laminating process oflaminating a plurality of sheet-like raw material elements 6 (includingat least one piece of an internal electrode 11) to form a piezoelectricelement 7 (shown in FIGS. 15(a) and 15(b)), a pressing process ofimparting pressing forces to the piezoelectric element 7 in verticalpressing directions using a die 8 to have the piezoelectric element 7molded into a predetermined shape to produce a piezoelectric element 7 a(shown in FIG. 15(c)), a burning process of burning the piezoelectricelement 7 a to produce a piezoelectric device 1 (shown in FIGS. 15(d)and 15(e)), and an electrode forming process of forming an externalelectrode 10 and an extension electrode 12 for the piezoelectric device1 thus produced (shown in FIG. 15(f)).

As shown in FIG. 15, the raw material elements 6, made of apiezoelectric material, a binding agent, and the like, are flexible andcapable of being deformed when pressing forces are imparted to the rawmaterial elements 6, as described hereinearlier. The die 8 is made of ametal material such as for example iron and/or the like, and has apredetermined shape so that the shape of the die 8 is transferred to thepiezoelectric element 7. In the pressing process, the die 8 is used toimpart pressing forces to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a piezoelectric element 7 a having apredetermined uneven thickness distribution. The shape of the die 8 isdesigned so that the piezoelectric element 7 is molded to form apiezoelectric device 1 having a predetermined uneven thicknessdistribution in view of a shrinkage caused by the burning process.

In the molding process, raw materials including piezoelectric ceramicpowders such as for example PZT powders are mixed with a binding agent(including a plasticizer, if required) and immersed in a solvent. Aplurality of raw material elements are then extracted from the solventby way of, for example, a Doctor Blade technique to form a plurality ofsheet-like raw material elements 6 each having a thickness in a range ofa few ten microns to a few hundred microns, and a unique width ifrequired.

In the laminating process, one or more sheet-like raw material elements6 are laminated to form a piezoelectric element 7. Similar to the firstembodiment of the producing process, the number and the thicknesses ofsheet-like raw material elements 6 to be laminated are calculated inaccordance with the thickness distribution of the piezoelectric device 1in view of a shrinkage caused by the burning process so as to obtain apiezoelectric device 1 having a predetermined thickness distributionafter the burning process. In the present embodiment, a plurality ofsheet-like raw material elements 6 are laminated in a manner that thewidths of the sheet-like raw material elements 6 decreases from a lowlayer toward a top layer on the both end portions. On a surface of thesheet-like raw material element 6, an internal electrode 11 made of anelectrode material such as, for example, platinum paste capable ofresisting high temperatures during the burning process is formed (shownin FIG. 15(a)). The position of the sheet-like raw material element 6having the internal electrode 11 should be determined so that theinternal electrode 11 is placed at a predetermined position of thepiezoelectric device 1 with respect to the thickness direction after theburning process. Further, the position and the size of the internalelectrode 11 on the surface of the sheet-like raw material element 6should be determined so that the internal electrode 11 could beelectrically connected with a signal wire, not shown in FIG. 15, toreceive an electric signal therefrom. In FIG. 15, the internal electrode11 is placed a little to the right side of the sheet-like raw materialelement 6 and not protruded from the left side of the sheet-like rawmaterial element 6 so that the internal electrode 11 is connected withthe signal wire on the right side of the piezoelectric device 1, andunexpected problem such as a short circuit would not occur on the leftside of the piezoelectric device 1.

In the pressing process, a die 8 made of a metal material such as forexample aluminum, brass, and/or the like, having a solidity required forthe pressing process, and capable of being easily worked, is used toimpart pressing forces to the piezoelectric element 7 as shown in FIG.15(c). In the present embodiment, the die 8 has two vertical pressingsurfaces opposing to each other and to be held in pressing contact withthe piezoelectric element 7 in vertical directions. Using the die 8,pressing forces are imparted to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a piezoelectric element 7 a havingan uneven thickness distribution concavely curved in a manner that thethickness of the piezoelectric element 7 a gradually increases from acenter portion toward end portions, and an internal electrode 11 spacedapart from and substantially in parallel relationship to the bottomsurface as shown in FIG. 15(d). As will be seen from the foregoingdescription, the present embodiment of the producing method, in whichthe die 8 is made of a metal material capable of being molded into adesired shape, and the vertical sides of the piezoelectric element 7 areheld in pressing contact with the vertical pressing surfaces of the die8 while the pressing forces are imparted so that the shape of the die 8is simply transferred to them can prevent the piezoelectric device 1from being damaged as well as constantly produce a plurality ofpiezoelectric devices with high precision.

In the burning process, the piezoelectric element 7 a is not processedby any machining means such as for example grinding means, but burned toproduce a piezoelectric device 1 having a predetermined uneven thicknessdistribution. In this manner, a plurality of piezoelectric devices canbe constantly produced with high precision because of the fact that theshape of the die 8 is simply transferred to them.

In the electrode forming process, an external electrode 10 made of, forexample, baking silver, gold sputter-coated material, and/or the like,is formed on a plane bottom surface of the piezoelectric device 1 afterthe burning process as shown in FIG. 15(f). Further, an extensionelectrode 12 is formed for ease in electrical connection with theinternal electrode 11. The extension electrode 12 is electricallyconnected with the internal electrode 11 on the right side surface ofthe piezoelectric device 1A, and extending therefrom to the bottomsurface along the right side surface of the piezoelectric device 1A. Theextension electrode 12 is made of, for example, baking silver, goldsputter-coated material, and/or the like, on the piezoelectric device 1having a desired shape.

As will be seen from the foregoing description, it is to be understoodthat the present embodiment of the producing method can produce apiezoelectric device 1A having a predetermined thickness distributionwith ease and increased flexibility by selectively increasing the numberof the raw material elements 6 to be laminated for a thick portion.

Though it has been described in the present embodiment that thepiezoelectric device 1A thus produced has a concave surface having athickness concavely curved in a manner that the thickness of the surfacegradually increases from a center portion toward end portions, the sameeffect can still be obtained even when the surface of the piezoelectricdevice 1A has an arbitrary shape such as for example a convex surface,convexo-concave surface, or the like, by selectively increasing thenumber of the raw material elements 6 to be laminated for a thickportion without restricting the shape of the piezoelectric device 1A.

Furthermore, though it has been described in the present embodiment thatthe piezoelectric device 1 thus produced is in the form of aquadrilateral sheet shape, the same effect can still be obtained evenwhen the piezoelectric device is in the form of an arbitrary shape suchas, for example, a disc sheet shape, by adaptively modifying the shapesof the raw material elements 6 and the die 8 in accordance with thedesired shape of the piezoelectric device.

Furthermore, while it has been described in the present embodiment thata plurality of raw material elements 6 are laminated to produce apiezoelectric device 1 in a manner that the widths of the raw materialelements 6 decreases from a low layer toward a top layer on the both endportions, the same effect can still be obtained even when a plurality ofraw material elements 6 equal in width or shape to one another arelaminated on the both ends to produce a piezoelectric element 7 as shownin FIGS. 16(a) and 16(b). In such a case, a laborious work of carefullylaminating the raw material elements 6 in accordance with their widthsis eliminated, and the shapes of the raw material elements 6 to belaminated are not restricted by the reason that the number of the rawmaterial elements 6 to be laminated can be selectively increased for athick portion.

[Eighth Embodiment]

Referring then to FIG. 17 of the drawings, there is shown an eighthpreferred embodiment of a method of producing a piezoelectric device 1.The present embodiment of the producing method is different from theseventh embodiment of the producing method in the fact that at least onepiece of sheet-like raw material element 6, and two or more pieces ofraw material elements 6 respectively formed with through bores differentin size to one another are molded, and at least one piece of internalelectrode 11 is intervening between at least two pieces of the rawmaterial elements 6 thus molded. The present embodiment of the producingmethod has additional effects of being capable of producing apiezoelectric device 1 or 1A having predetermined thickness and shapedistributions with ease and increased flexibility as well as realizingan even polarization, thereby protecting the piezoelectric device frombeing cracked.

Similar to the fifth embodiment, the present embodiment of thepiezoelectric device 1 has a thickness concavely curved in a manner thatthe thickness of the piezoelectric device 1 gradually increases from acenter portion toward end portions along lateral directions. Thepiezoelectric device 1 further comprises an external electrode 10 formedon a plane bottom surface of the piezoelectric device 1, an internalelectrode 11 formed inside of the piezoelectric device 1 and spacedapart from and substantially in parallel relationship to the externalelectrode 10, and an extension electrode 12 extending from the internalelectrode 11 to the bottom surface of the piezoelectric device 1 througha side surface of the piezoelectric device 1.

Similar to the first embodiment of the producing process, in the presentembodiment, a process of producing a piezoelectric device 1 comprises: amolding process of molding raw materials such as for examplepiezoelectric ceramic powders to form a plurality of sheet-like rawmaterial elements 6 (not shown in FIG. 17), a die-cutting process ofdie-cutting the sheet-like raw material elements, as many as required,to obtain a plurality of window frame-like raw material elements 6respectively formed with through bores in the form of rectangular windowshapes (not shown in FIG. 17), a laminating process of laminating aplurality of window frame-like raw material elements 6 and a pluralityof sheet-like raw material elements 6 ((including at least one piece ofan internal electrode 11) to form a piezoelectric element 7A (shown inFIGS. 17(a) and 17(b)), an edge cutting process of cutting off the frontend rear edges (unwanted parts) of the piezoelectric element 7A (shownin FIG. 17(c)) to obtain a piezoelectric element 7, a pressing processof imparting pressing forces using a die 8 to the piezoelectric element7 in vertical pressing directions to have the piezoelectric element 7molded into a predetermined shape to obtain a piezoelectric element 7 a(shown in FIG. 17(d)), a burning process of burning the piezoelectricelement 7 a (shown in FIGS. 17(e) and 17(f)), and an electrode formingprocess of forming an external electrode 10 and an extension electrode12 for the piezoelectric device 1 thus produced (shown in FIG. 17(g)).

As shown in FIG. 17, the raw material elements 6, made of apiezoelectric material, a binding agent, and the like, are flexible andcapable of being deformed when pressing forces are imparted to the rawmaterial elements 6, as described hereinearlier. The die 8 is made of ametal material such as for example iron and/or the like, and has apredetermined shape so that the shape of the die 8 is transferred to thepiezoelectric element 7. In the pressing process, the die 8 is used toimpart pressing forces to the piezoelectric element 7 to have thepiezoelectric element 7 molded into a piezoelectric element 7 a having apredetermined uneven thickness distribution. The shape of the die 8 isdesigned so that the piezoelectric element 7 is molded to form apiezoelectric device 1 A having a predetermined uneven thicknessdistribution in view of a shrinkage caused by the burning process.

In the molding process, raw materials including piezoelectric ceramicpowders such as for example PZT powders are mixed with a binding agent(including a plasticizer, if required) and immersed in a solvent. Aplurality of raw material elements are then extracted from the solventby way of, for example, a Doctor Blade technique to form a plurality ofsheet-like raw material elements 6 each having a thickness in a range ofa few ten microns to a few hundred microns, and a unique width ifrequired.

In the die-cutting process, the sheet-like raw material elements, asmany as required, are die-cut to obtain a plurality of window frame-likeraw material elements 6 respectively formed with through bores differentin shape and size.

In the laminating process, one or more sheet-like raw material elements6 including window frame-like raw material elements 6 as shown in FIG.17(a) are laminated to form a piezoelectric element 7A as shown in FIG.17(b). Here, the number and the thicknesses of sheet-like raw materialelements 6 to be laminated are calculated in accordance with thethickness distribution of the piezoelectric device 1 in view of ashrinkage caused by the burning process so as to obtain a piezoelectricdevice 1 having a predetermined thickness distribution after the burningprocess. On a surface of one sheet-like raw material element 6, aninternal electrode 11 is formed as described hereinearlier. In thepresent embodiment, the piezoelectric device 1 has a thickness concavelycurved in a manner that the thickness of the piezoelectric device 1gradually increases from a center portion toward end portions along theminor axis. One or more sheet-like raw material elements 6 respectivelyformed with through-bores are laminated in a manner that the throughbores of the one or more sheet-like raw material elements 6 to belaminated should be in size collectively in accordance with thethickness distribution of the piezoelectric device 1. This means that aplurality of window frame-like raw material elements 6 are laminated ina manner that the widths of the window frame-like raw material elements6 gradually decreases from a low layer toward a top layer on the bothend portions to form a piezoelectric element 7A as shown in FIG. 17(b).Similar to the first embodiment of the producing process, while beinglaminated, the sheet-like raw material elements 6 may be pressed andheated if required.

Preferably, the raw material elements 6 may be made in a manner that theouter edges of the raw material elements 6 are equal in shape (size) toone another so that the raw material elements 6 can be easily laminatedwithout displacements simply after positioning the sheet-like rawmaterial elements 6 with respect to their respective outer edges.Alternatively, each of the raw material elements 6 may have at least oneperpendicular edge in a manner that the raw material elements 6 havethrough bores accurately die-cut with respect to their perpendicularedges so that the raw material elements 6 can be easily laminatedwithout displacements simply after positioning the perpendicular edgesof the raw material elements 6 although the raw material elements 6 arenot equal in shape to one another. Furthermore, the raw materialelements 6 may be laminated in a manner that the through bores of theraw material elements 6 in size collectively correspond to the thicknessdistribution of the piezoelectric device 1 along a width direction (inthe present embodiment, the raw material elements 6 are laminated in amanner that the size of each of the through bores of the raw materialelements 6 gradually increases along the width direction from the lowerlayer to the top layer) so as to form the piezoelectric element 7Ahaving a thickness concavely curved in a manner that the thickness ofthe piezoelectric element 7A gradually increases from a center portiontoward end portions along the minor axis.

In the edge cutting process, unwanted parts of the piezoelectric element7A collectively constituted by the raw material elements 6 are cut off.The unwanted parts of the piezoelectric element 7A may not be cut offbut used as reinforcing parts in the case that the piezoelectric element7A has such an extremely thin portion that the piezoelectric element 7Aas a whole would be abnormally curved and fail to lose its shape whenthe unwanted parts of the piezoelectric element 7A are cut off. In thiscase, the unwanted parts of the piezoelectric element 7A may be cut offafter the pressing process or the burning process.

In the pressing process, similar to the first embodiment of theproducing process, a die 8 made of a metal material such as for exampleiron and/or the like is used to impart pressing forces to thepiezoelectric element 7 in thickness directions as shown in FIG. 17(d)to have the piezoelectric element 7 molded into a piezoelectric element7 a having a predetermined uneven thickness distribution as shown inFIG. 17(e). In the present embodiment of the producing method, thepressing forces imparted by the die 8 to the piezoelectric element 7 arerestricted to a certain degree, the piezoelectric element 7 is preventedfrom being unnecessarily and abnormally deformed, and a residual stressremaining in the piezoelectric element 7 a is reduced by the reason thatthe piezoelectric element 7 laminated in the previous laminating processhas a shape approximately similar to the thickness distribution of thepiezoelectric device 1 as shown in FIG. 17(c). Furthermore, the presentembodiment of the producing method can advantageously produce apiezoelectric device whose thickness distribution is so large (thedifference between its thin portion and thick portion is extremelylarge) that the thickness distribution cannot be formed by simplydeforming the piezoelectric element 7.

In the burning process, similar to the first embodiment of the producingprocess, the piezoelectric element 7 a is not processed by any machiningmeans such as for example grinding means, but burned to produce apiezoelectric device 1 having a predetermined uneven thicknessdistribution. In this manner, a plurality of piezoelectric devices canbe constantly produced with high precision because of the fact that theshape of the die 8 is simply transferred to them.

In the electrode forming process, an external electrode 10 made of, forexample, baking silver, gold sputter-coated material, and/or the like,is formed on a plane bottom surface of the piezoelectric device 1 afterthe burning process. Further, an extension electrode 12 is formed forease in electrical connection with the internal electrode 11. Theextension electrode 12 is electrically connected with the internalelectrode 11 on the right side surface of the piezoelectric device 1A,and extending therefrom to the bottom surface along the side surface ofthe piezoelectric device 1A. The extension electrode 12 is made of, forexample, baking silver, gold sputter-coated material, and/or the like,on the piezoelectric device 1 having a desired shape.

Though it has been described in the present embodiment that thepiezoelectric device 1 thus produced has a concave surface having athickness concavely curved in a manner that the thickness of the surfacegradually increases from a center portion toward end portions, the sameeffect can still be obtained even when the surface of the piezoelectricdevice has an arbitrary shape such as for example a convex surface,convexo-concave surface, or the like, by selectively increasing thenumber of the raw material elements 6 to be laminated for a thickportion 1 in view of the positions, the sizes, and the number of theirthrough bores without restricting the shape of the piezoelectric device.

Furthermore, though it has been described in the present embodiment thatthe unwanted parts of the piezoelectric element 7A are cut off by thereason that the piezoelectric device 1 thus produced should have aconcave surface having a thickness concavely curved in a manner that thethickness of the surface gradually increases from a center portiontoward end portions (two directions), the same effect can still beobtained even when the piezoelectric device 1 thus produced has aconcave surface having a thickness concavely curved in a manner that thethickness of the surface gradually increases from a center portiontoward end portions as shown in FIGS. 6 and 7. In such a case, thepiezoelectric element 7A has no unwanted parts to be cut off, and theedge cutting process is accordingly eliminated.

Furthermore, while it has been described in the present embodiment thata plurality of raw material elements 6 are laminated to obtain apiezoelectric element 7A similar in shape to the piezoelectric device 1to be produced in a manner that the widths of through bores of the rawmaterial elements 6 increases from a low layer toward a top layer, thesame effect can still be obtained even when a plurality of raw materialelements 6 respectively having through bores equal in width or shape toone another as shown in FIG. 18(a) are laminated to produce apiezoelectric element 7A as shown in FIG. 18(b) as long as thepiezoelectric element 7A is similar in shape to the piezoelectric device1 or 1A to be produced, and the number of the raw material elements 6 tobe laminated is selectively increased for a thick portion in view of thepositions, the sizes, and the number of their through bores. In such acase, a laborious work of selectively laminating the raw materialelements 6 in accordance with the widths of their through bores iseliminated without restricting the shape of the piezoelectric device 1.

Though it has been described in the previous embodiments (shown in FIG.12 through 18) that the piezoelectric device comprises an extensionelectrode 12 extending from the internal electrode 11 to the bottomsurface of the piezoelectric device 1 through the side surface of thepiezoelectric device, the same effect can still be obtained even whenthe extension electrode 12 is formed only on the side surface of thepiezoelectric device, or the internal electrode 11 protruded from theside surface of the piezoelectric device is directly connected with asignal wire in place of the extension electrode 12 as long as theinternal electrode 11 can have an electrical connection with the signalwire without restricting the construction of the piezoelectric device 1or 1A.

Though it has been described in the previous embodiments (shown in FIG.12 through 18) that the piezoelectric device comprises an internalelectrode 11 of a single layer, the same effect can still be obtainedeven when the piezoelectric device comprises a plurality of internalelectrodes 11 constituted by a plurality of layers each having apredetermined thickness as shown in FIG. 19.

[Ninth Embodiment]

Referring to FIG. 20 of the drawings, there is shown a ninth preferredembodiment of an ultrasonic probe having a piezoelectric device 1C ofany one of the first to fourth embodiments according to the presentinvention.

As shown in FIG. 20, the piezoelectric device 1C further comprises anacoustic matching layer 2 for effectively receiving and transmitting anultrasonic wave, and a rearward load 4, placed rearward of thepiezoelectric device 1C, for carrying out an acoustic damping operation.The piezoelectric device 1C further comprises a signal wire 13 made of,for example, FPC (Flex Print Cables), for electrically connecting anexternal electrode 10 formed on the bottom surface of the piezoelectricdevice 1C with an apparatus such as, for example, an ultrasonicdiagnostic apparatus, a nondestructive testing apparatus, or the likethrough a cable, not shown. The piezoelectric device 1C furthercomprises a ground wire 14 for electrically connecting an externalelectrode 10 formed on the upper surface of the piezoelectric device 1Cwith an apparatus such as, for example, an ultrasonic diagnosticapparatus, a nondestructive testing apparatus, or the like through acable, not shown.

As will be seen from the foregoing description, it is to be understoodthat the ninth embodiment of the ultrasonic probe according to thepresent invention, comprising a piezoelectric device 1 as described inany one of the first through fourth embodiments can reliably operatewithout being influenced by differences among piezoelectric devices.This means that the present embodiment of the ultrasonic probe,comprising a piezoelectric device 1C, which has been produced not bycarrying out any technically-difficult machining processing but bysimply transferring the shape of the die thereto can protect thepiezoelectric device from being microcracked, and ensure that theultrasonic probe stably maintains its performances. The producing methodof any one of the first through fourth embodiments is appropriate forconstantly producing a plurality of piezoelectric devices with highprecision because of the fact that the shape of the die 8 is simplytransferred to them. This leads to the fact that the present embodimentof the ultrasonic probe can reliably operate without being influenced bydifferences among piezoelectric devices.

Though it has been described in the present embodiment that thepiezoelectric device 1C comprises an acoustic matching layer 2 of asingle layer, the same effect can still be obtained even when theacoustic matching layer 2 is constituted by a plurality of layers.

Though it has been described in the present embodiment that the signalwire 13 is electrically connected with an external electrode 10 b formedon the bottom surface of the piezoelectric device 1C, and the groundwire 14 is electrically connected with an external electrode 10 a formedon the upper surface of the piezoelectric device 1C, the same effect canstill be obtained even when the signal wire 13 is electrically connectedwith the external electrode 10 a formed on the upper surface of thepiezoelectric device 1C, and the ground wire 14 is electricallyconnected with the external electrode 10 b formed on the bottom surfaceof the piezoelectric device 1C.

Furthermore, through it has been described in the present embodimentthat the ultrasonic probe comprises no acoustic lens 3 described in theprior art (shown in FIG. 24), the same effect can still be obtained evenwhen the ultrasonic probe comprises an acoustic lens 3.

[Tenth Embodiment]

Referring to FIG. 21 of the drawings, there is shown a tenth preferredembodiment of an ultrasonic probe. The present embodiment of theultrasonic probe is different from the ninth embodiment of theultrasonic probe in the fact that the ultrasonic probe comprises apiezoelectric device 1A of any one of the fifth to eighth embodimentsaccording to the present invention. The ultrasonic probe thusconstructed can stably transmit and receive ultrasonic waves, protectthe piezoelectric device 1A from being microcracked, and ensure that theultrasonic probe maintains its performances by the reason that thepiezoelectric device 1A is kept from being excessively distorted whilethe piezoelectric device is driven. The same constitutional elements aresimply represented by the same reference numerals as those of the ninthembodiment, and will be thus omitted from the following description.

As shown in FIG. 21, the ground wire 14 is electrically connected withan extension electrode 12 on the bottom surface of the piezoelectricdevice 1A. The extension electrode 12 is electrically connected with theinternal electrode 11 of the piezoelectric device 1A. The externalelectrode 10 and the internal electrode 11 are spaced apart from andsubstantially in parallel relationship with each other. The presentembodiment of the piezoelectric device 1A thus constructed is designedto be evenly polarized.

Though it has been described in the present embodiment that thepiezoelectric device comprises an acoustic matching layer 2 constitutedby a single layer, the same effect can still be obtained even when theacoustic matching layer 2 is constituted by a plurality of layers.

Though it has been described in the present embodiment that the signalwire 13 is electrically connected with an external electrode 10 formedon the bottom surface of the piezoelectric device 1A, and the groundwire 14 is electrically connected with an internal electrode 11 upwardlyspaced apart from the external electrode 10, the same effect can stillbe obtained even when the signal wire 13 is electrically connected withthe internal electrode 11, and the ground wire 14 is electricallyconnected with the external electrode 10.

Furthermore, through it has been described in the present embodimentthat the ultrasonic probe comprises no acoustic lens 3 described in theprior art (shown in FIG. 24), the same effect can still be obtained evenwhen the ultrasonic probe comprises an acoustic lens 3.

[Eleventh Embodiment]

Referring to FIG. 22 of the drawings, there is shown an eleventhpreferred embodiment of an ultrasonic diagnostic apparatus 16 accordingto the present invention, comprising an ultrasonic probe 15 of any oneof the ninth embodiment (shown in FIG. 20) and tenth embodiment (shownin FIG. 21) according to the present invention. The ultrasonic probe 15is electrically connected with a main body of the ultrasonic diagnosticapparatus 16 through a cable. The ultrasonic probe of any one of theninth and tenth embodiments has an advantage of stably operating withoutbeing influenced by differences among piezoelectric devices as describedhereinearlier.

As will be seen from the foregoing description, it is to be understoodthat the present embodiment of the ultrasonic diagnostic apparatus 16according to the present invention, comprising an ultrasonic probe 15 ofany one of the ninth embodiment and tenth embodiment can carry out anultrasound diagnosis with high reliability, taking the advantage of theultrasonic probe 15.

Though it has been described in the present embodiment that theultrasonic probe 15 is electrically connected with a main body of theultrasonic diagnostic apparatus 16 through a cable, the same effect canstill be obtained even when the ultrasonic probe 15 is remotelycontrolled by the main body of the ultrasonic diagnostic apparatus 16without wires.

[Twelfth Embodiment]

Referring to FIG. 23 of the drawings, there is shown an twelfthpreferred embodiment of a nondestructive testing apparatus 17 accordingto the present invention, comprising an ultrasonic probe 15 of any oneof the ninth embodiment (shown in FIG. 20) and tenth embodiment (shownin FIG. 21) according to the present invention. The ultrasonic probe 15is electrically connected with a main body of the nondestructive testingapparatus 17 through a cable. The ultrasonic probe of any one of ninthand tenth embodiments has an advantage of stably operating without beinginfluenced by differences among piezoelectric devices as describedhereinearlier.

As will be seen from the foregoing description, it is to be understoodthat the present embodiment of the nondestructive testing apparatus 17according to the present invention, comprising an ultrasonic probe 15 ofany one of the ninth embodiment and tenth embodiment can stably carryout a nondestructive test with high reliability, taking the advantage ofthe ultrasonic probe 15.

Though it has been described in the present embodiment that theultrasonic probe 15 is electrically connected with a main body of thenondestructive testing apparatus 17 through a cable, the same effect canstill be obtained even when the ultrasonic probe 15 is remotelycontrolled by the main body of the nondestructive testing apparatus 17without wires.

From the foregoing description, it is to be understood that thepiezoelectric device according to the present invention, producedthrough the processes of mixing a piezoelectric material with a bindingagent to form a plurality of raw material elements, and impartingpressing forces to piezoelectric element 7 constituted by the laminatedraw material elements to have the piezoelectric element 7 molded into apredetermined shape, has a predetermined thickness distribution and isaccurate in dimension. Furthermore, the method of producing apiezoelectric device according to the present invention, comprising thesteps of mixing a piezoelectric material with a binding agent to form aplurality of raw material elements, imparting pressing forces topiezoelectric element 7 constituted by the laminated raw materialelements to have the piezoelectric element 7 molded into a predeterminedshape can produce a plurality of piezoelectric devices each having athickness distribution with high precision, thereby eliminating the needof carrying out any complicated machining processing such as for examplea grinding processing.

1. (Deleted)
 2. A method of producing a piezoelectric device, comprisingthe steps of: (a) molding one or more raw material elements including atleast one piezoelectric material to form a predetermined piezoelectricelement; and (b) imparting pressing forces to said piezoelectric elementto have said piezoelectric element molded into a predetermined shape,and in which said step (a) has a step of laminating a plurality ofsheet-like raw material elements respectively having thicknessescollectively in accordance with a thickness distribution of saidpiezoelectric device.
 3. A method of producing a piezoelectric device asset forth in claim 2, in which said step (a) has a step of laminatingthe number of sheet-like raw material elements in accordance with athickness distribution of said piezoelectric device.
 4. A method ofproducing a piezoelectric device as set forth in claim 2, in which saidstep (a) has a step of laminating one or more sheet-like raw materialelements respectively having shapes collectively in accordance with athickness distribution of said piezoelectric device.
 5. A method ofproducing a piezoelectric device as set forth in claim 4, in which saidstep (a) has a step of laminating one or more sheet-like raw materialelements respectively having widths collectively in accordance with athickness distribution of said piezoelectric device.
 6. A method ofproducing a piezoelectric device as set forth in claim 2, in which saidstep (a) has a step of laminating one or more sheet-like raw materialelements respectively formed with through bores.
 7. A method ofproducing a piezoelectric device as set forth in claim 6, in which saidstep (a) has a step of laminating one or more sheet-like raw materialelements respectively formed with through bores in size collectively inaccordance with a thickness distribution of said piezoelectric device.8. A method of producing a piezoelectric device as set forth in claim 2,in which said step (b) has a step of imparting pressing forces to saidpiezoelectric element in laminating directions and directionsperpendicular to said laminating directions.
 9. A method of producing apiezoelectric device, comprising the steps of: (c) producing a firstpiezoelectric body having a non-plane first surface and a plane secondsurface opposite to said first surface, and a second piezoelectric bodyhaving a plane first surface and a plane second surface opposite to saidfirst surface, said second piezoelectric body having electrodesrespectively on said first and second surfaces; and (d) fixedlyconnecting said first piezoelectric body to said second piezoelectricbody with said second surface of said first piezoelectric body held incontact with said first surface of said second piezoelectric body. 10.(Deleted)
 11. A piezoelectric device, comprising a piezoelectric elementhaving one or more raw material elements including a piezoelectricmaterial, in which pressing forces have been imparted to saidpiezoelectric element to have said piezoelectric element molded, andsaid piezoelectric element having a plurality of sheet-like raw materialelements respectively having thicknesses and laminated in accordancewith a thickness distribution of said piezoelectric device.
 12. Apiezoelectric device as set forth in claim 11, in which saidpiezoelectric element has a plurality of sheet-like raw materialelements respectively formed with through bores, and laminated inaccordance with a thickness distribution of said piezoelectric device.13. A piezoelectric device as set forth in claim 11, in which saidpiezoelectric element has a sheet-like raw material element formed witha through bore in size in accordance with a thickness distribution ofsaid piezoelectric device.
 14. A piezoelectric device as set forth inclaim 11, in which said piezoelectric element has a plurality oflaminated sheet-like raw material elements and a plurality of electrodesspaced apart from one another at a predetermined distance.
 15. Anultrasonic probe having a piezoelectric device as set forth in claim 11.16. An ultrasonic diagnostic apparatus having an ultrasonic probe as setforth in claim
 15. 17. A nondestructive testing apparatus having anultrasonic probe as set forth in claim 15.